Turning to FIG. 1, an example of a conventional DLL 100 can be seen. In operation, DLL 100 is able to generate multiple phases DCLK1 to DCLKN of clock signal from taps within delay line 108. To accomplish this, a phase/frequency detector (PFD) compares the clock signal CLK to the output from the end of the delay line 108 to generate charge pump control signals UP and DOWN. These up control signals UP and DOWN vary the charge on the loop filter or low pass filter (LPF) 106, which, in turn, varies the control signal CNTL to achieve phase lock. This DLL 100, however, is ill-suited to provide high speed, narrow pulses (i.e., 25 ps pulses spanning a 400 ps window) because of the delay used to achieve phase lock and because the DLL 100 is continuously operating even when the pulses are not used. Thus, there is a need for an improved DLL that can generate high speed, narrow pulses for applications like terahertz radar systems.
Some examples of conventional circuits are: Williams, “Filling the THz Gap,” doi:10.1088/0034-4885/69/2/R01; Heydari et al., “Low-Power mm-Wave Components up to 104 GHz in 90 nm CMOS,” ISSCC 2007, pp. 200-201, February 2007, San Francisco, Calif.; LaRocca et al., “Millimeter-Wave CMOS Digital Controlled Artificial Dielectric Differential Mode Transmission Lines for Reconfigurable ICs,” IEEE MTT-S IMS, 2008; Scheir et al., “A 52 GHz Phased-Array Receiver Front-End in 90 nm Digital CMOS” JSSC December 2008, pp. 2651-2659; Straayer et al. “A Multi-Path Gated Ring Oscillator TDC With First-Order Noise Shaping,” IEEE J. of Solid State Circuits, Vol. 44, No. 4, April 2009, pp. 1089-1098; Huang, “Injection-Locked Oscillators with High-Order-Division Operation for Microwave/Millimeter-wave Signal Generation,” Dissertation, Oct. 9, 2007; Cohen et al., “A bidirectional TX/RX four element phased-array at 60 GHz with RF-IF conversion block in 90 nm CMOS processes,” 2009 IEEE Radio Freq. Integrated Circuits Symposium, pp. 207-210; Koh et al., “A Millimeter-Wave (40-65 GHz) 16-Element Phased-Array Transmitter in 0.18-μm SiGe BiCMOS Technology,” IEEE J. of Solid State Circuits, Vol. 44, No. 5, May 2009, pp. 1498-1509; York et al., “Injection- and Phase-locking Techniques for Beam Control,” IEEE Transactions on Microwave Theory and Techniques, Vol. 46, No. 11, November 1998, pp. 1920-1929; Buckwalter et al., “An Integrated Subharmonic Coupled-Oscillator Scheme for a 60-GHz Phased Array Transmitter,” IEEE Transactions on Microwave Theory and Techniques, Vol. 54, No. 12, December 2006, pp. 4271-4280; PCT Publ. No. WO2009028718; U.S. Pat. No. 7,157,949; and U.S. Pat. No. 7,295,053.